Sculpt brush isn't drawing much detail
As you can read on the upper right corner of your window, you,ve got 29.641 vertex, it's not enough for fine details. Try subdividing until you reach 1.000.000.
In object mode switch to "Smooth Shading".
If the computer gets slow, subdivide you model in different objects (P key in edit mode mode), and sculpt them one by one, using the multiresolution modifier to swithc between different levels of details.